Electrolytic codeposition of fine particles with copper

ABSTRACT

FINE PARTICLES OF MANY NON-CONDUCTING MATERIALS DO NOT CODEPOSIT READILY FROM AQUEOUS ACIDIC COPPER ELECTROPLATING BATHS, UNLESS THERE IS PRESENT IN THE BATH ALIPHATIC AMINES, ESPECIALLY POLYAMINES OR IMINES, OR AMINO ACIDS SUCH AS ALANINE OR EDTA. THESE AMINO COMPOUNDS ARE ESPECIALLY EFFECTIVE IN ACID COPPER SULFATE PLATING BATHS FOR THE CODEPOSITION OF DISPERSED FINE, BATH-INSOLUBLE, NONCONDUCTING PARTICLES. THESE 2-PHASE COMPOSITE COPPER PLATES HAVE ENGINEERING USE POSSIBLITIES FOR ANTI-FRICTION AND ANTI-SEIZING PROBLEMS.

United States Patent ELECTROLYTIC CODEPOSITION OF FINE PARTICLES WITHCOPPER Thaddeus W. Tomaszewski and Lillie C. Tomaszewski,

Dearborn, Mich., assignors to Udylite Corporation,

Warren, Mich.

.No Drawing. Filed June 19, 1969, Ser. No. 834,891

' Int. Cl. C23b 5/48, 5/20 US. Cl. 204'16 16 Claims ABSTRACT OF THEDISCLOSURE This invention relates to the cathodic codeposition ofmultitudinous fine particles of bath-insoluble, non-conducting,inorganicand organic powders dispersed in aqueous acidic copper plating baths.More particularly this invention provides a means to improve anduniformly increase-the degree of codeposition of bath-dispersedinorganic and organic particles throughout the electrodeposited copperplate.

The densely codeposited inorganic fine particles in the matrix of theelectrodeposited copper can increase the tensile strength of the copperand its resistance to high temperature creep, and the inorganic andorganic particles can greatly decrease the tendency for copper surfacesto stick and seize, yet without causing any appreciable loss inelectrical or heat conductivity.

Thus,. these copper deposits can be used for various engineeringpurposes either as a composite copper plate on top of a basis metal,including wire or strip, or as an electroform.

It has now been found that amines, especially aliphatic amines, promotethe codeposition of bath-insoluble, nonconducting particles dispersed(for example, by air agitation) in the acidlcopper electroplating baths.The most effective aliphatic amines for promoting the codepositionare'polyamines and polyimines such as ethylene diamine, diethylene.triamine, tetraethylenepentamine, polyethylene' imine, etc. Theseamines when present in the standard acidic 'coppe'r plating baths ofeither low or high concentrations of copper ions make possible extensivecodeposition of dispersed fine bath-insoluble particles such as bariumsulfate, strontium sulfate, aluminum oxide, titanium oxide, zirconium'oxide, kaolin (a hydrous aluminum silicate rareearth fluorides, stannicoxide, finely powdered glass, lead sulfate, PVC, nylon, saran,polyethylene," polycarbonate, acetal; polystyrene, ABS, lead phosphate,"ceric oxide, boron nitride, graphite, molybden'um-sulfide, ironsilicide, silicon carbide, boron carbide, boron, silicon, silicondioxide, etc.

The most effective aliphatic amines, as mentioned, are the polyamines.For example, 0.1 g./l. of ethylene diamine is at least as effective as50 g./l. of ethyl amine in promoting the codeposition of the fine,insoluble particles on vertical surfaces. With 'tetraethylene pentamine,a concentration as low as 1 mg./l.- will make possible the codepositionof about 3.5 wt. percent of fine barium sulfate particles dispersed inthe acid copper sulfate plating bath. Without the amines present in thebath, practically no particles of the type shown above are codepositedon a vertical surface from acid copper plating baths. This is veryunlike codeposition of these fine particles dispersed in acidic nickelbaths where codeposition on vertical cathode surfaces occurs without theneed of special organic additives.

Besides the aliphatic amines mentioned, amino acids such as alanine,N,N-diethyl glycine, asparagine, N- methyl taurine, ethylene diaminetetra-acetic acid (-EDTA), and other amino acid and sequesterin agents,especially those with more than one amino group, give excellent resultsin promoting codeposition of fine, bathinsoluble, non-conductingparticles in the acid copper plating baths.

The bath-insoluble, fine powders are kept suspended and dispersed in theacid copper plating baths by means of mechanical or air agitation. Ingeneral, air agitation is preferred, and of course, the air must not becontaminated with oil. Optimum codeposition results are usually reachedwith concentrations of particles of about 25 to 150 g./l., though higherconcentration produce no troubles, and with some particles such asbarium sulfate and strontium sulfate, concentrations of 500 g./l. can beused. It is important that the fine particles are clean. For example,some commercial grades of talc (a hydrous magnesium silicate) had to bewashed with alcohol or acetone before the best codeposition resultscould be obtained. In general, the particle sizes may be from about 10microns down to 0.01 micron for the inorganic particles with thepreferred range of about 5 microns down to 0.01 micron. With particlesmuch greater than about 10 microns, roughness from the inorganicparticles is obtained on areas on which settling can occur. Someagglomerated powders may have apparent larger particle size than thepreferred size, but with agitation in the copper bath, the largeragglomerates are usually broken down and particles of about 5 micronsdiameter and under may then be the predominant size. With organic resinpowders the particle size may be as high as 50 microns size and stillcodeposit smoothly on vertical surfaces.

The pH of the acid copper plating baths unlike with nickel, does nothave a profound effect on the percentage of the powder codeposited inthe copper matrix. An acid copper sulfate bath having 100 or 200 g./l.of sulfuric acid and low or high concentrations of copper sulfate,yields in general very similar percentages of codeposition as does acopper bath with only 1 g./l. of sulfuric acid. This is also true foracidic copper plating such as copper sulfamate, copper methanesulfonate, and copper fiuoborate. Large variation in the temperature ofthe acid copper plating baths does exert a pronounced influence on thepercentage of particles codeposited with the copper plate. At roomtemperatures or slightly lower there is maximum codeposition of theparticles on vertical surfaces in the presence of the aliphatic aminepromoters. As the temperature of the bath is increased, lesseo-deposits, and temperatures higher than 60 C. are not desirable. Beloware listed some specific examples illustrating the codeposition ofparticles with copper according to this invention.

EXAMPLE I Concentration in grams per liter CuSO .5H O 75-250. H 50'0-150. Tetraethylene pentamine 0.001-1. BaSO, fine powder 10-150.Temperature60120 F. Agitationair or mechanical.

Current density 10-100 amps/sq. ft.

The maximum codeposition was about 5.5 wt. percent on vertical surfaceswith higher concentrations on settling surfaces. In Example I, if finezirconium oxide powder is used in concentrations of about 1-30() g./l.instead of the barium sulfate powder, a maximum of about 6 wt. percentwas obtained on vertical surfaces. With fine titania powder the maximumcodeposition on vertical surfaces was about 4%.

EXAMPLE ]1 Concentration in grams per liter CuSO .5H ,O 100-250. H 80-100. EDTA 1-15.

Cerium oxide fine powder -150.

Temperature60l20 F. Agitationair or mechanical.

Current density 10-100 amps/sq. ft.

The maximum codeposition was about 3.5 wt. percent on vertical surfaces.If fine silicon carbide powder (0.1 to 7 microns) is used instead of thecerium oxide in Example II, the maximum codeposition on verticalsurfaces was around 4 Wt. percent, but on settling surfaces it was muchhigher.

EXAMPLE III The procedure of Example I is repeated with the exceptionthat finely divided polyvinyl chloride (PVC), of a particle size Withinthe range of about l-20 microns, is substituted for the barium sulfate.Using this procedure, comparable results are obtained.

In acidic copper fluoborate baths, the codeposition of the samedispersed inorganic particles in general proceeds very well, however,the addition of the amines or amino acids maximizes the codepositionrate. In the case of conducting and semi-conducting particles such asgraphite and molybdenum sulfide, the codeposition proceeds very readilyin the acidic copper plating baths, and it would seem that there is noneed to use the amines or amino acid promoters. Nevertheless with thesepromoters present, lower concentrations of these fine particles may beused which in these cases tend to minimize roughness troubles. That is,with these powders it is difficult to get smooth plate with theircodeposition, though with the use of the promoters and with the use ofthe finest particles, the plate is them much smoother. With fineparticles of such powders as barium sulfate, titania, alumina, siliconcarbide, the plates are very smooth.

In some cases mixtures of particles for codeposition are desirable, forexample, barium sulfate with strontium sulfate, mica with bariumsulfate, graphite or molybdenum sulfide with barium sulfate, orstrontium sulfate.

Surfactants and brightening agents may be present in the acid copperplating baths which do not appreciably affect the ductility and adhesionof the deposits. When air agitation is used, the surfactants should notcause overfoaming, and preferably an eight carbon chain length should beused, such as sodium Z-ethyl hexyl sulfate, and sodium n-oetylsulfonate.

As mentioned, the most effective amine compounds for promotingcodeposition of particles are those where the amino group is attached toan aliphatic group, that is, the aliphatic amino compounds, and thisdesignation would apply even if an aromatic ring is in the molecule, asin benzyl amine. The most elfective amino compounds are the polyamino orpolyimine compounds such as ethylene diamine, diethylene triamine,tetraethylene pentarnine, etc. The aliphatic amino acids may havecarboxyl groups as in alanine and EDTA, sulfonic groups as in N-methyltaurine and phosphonic groups as in N(CH PO (OH) It is to be appreciatedthat as used herein, the term Saran is intended to refer topolyvinylidene chlorides; the term nylon is intended to refer topolyamides; and the terms Teflon and Kel-F are intended to refer tofluorocarbon resins, such as the polytetrafluoroethylenes.

What is claimed is:

trodepositing with copper fine bath-insoluble, substantiallynon-conducting particles dispersed in aqueous acidic copperelectroplating baths which contain dissolved therein additionally atleast one organic compound which contains at least one aliphatic aminogroup. 7

2. A method in accordance with claim '1 wherein said amino compound istetraethylene peutamine in a conoentIation greater than about 1milligram per liter. 1

3. A method in accordance with claim 1 wherein said amino compound is anamino acid in a concentration greater than about 0.1 gram per liter.

4. A method in accordance with claim 1 wherein said bath-insolubleparticles are barium sulfate particles in concentrations of at leastabout 1 gram/liter and of particle size less than about 5 microns.

5. A method in accordance with claim tions of at least about 1 gram perliterand particle size less than about 5 microns.

6. A method in accordance with claim 1 wherein said bath-insolubleparticles are silicon carbide particles in concentrations of at leastabout 1 gram/liter and par-,

ticle size less than about 7 microns.

7. -A method in accordance with claim 1 wherein said bath-insolubleparticles are aluminum oxide particles in concentrations of at leastabout 1 gram/liter and particle size less than about 5 microns. I

8. A method in accordance with claim 1 wherein said bath-insolubleparticles are polyvinylchloride (PVC) "particles in concentrations of atleast about 1 gram/liter and particle size less than about 50 microns.

9. An electroplating bath comprising anaqueous acidic copperelectroplating bath containing dispersed therein fine bath-insoluble,non-conducting particles and said cop per bath containing dissolvedtherein additionally atleast one organic compound which contains atleast one aliphatic amino group.

10. A bath in accordance with claim 9 wherein said amino compound istetraethylene pentarnine in a concentration greater than about 1milligram per liter.

11. A bath in accordance with claim 9 wherein said concentration aminocompound is an amino acid in a greater than about 0.1 gram/liter.

12. A bath in accordance with claim 9 wherein said: bath-insolubleparticles are barium sulfate particles fin concentrations of at leastabout 1 gram/liter and of article size less than about 5 microns.

13. A bath in accordance with claim, 9 whereinsaid bath-insolubleparticles are boron particles in concentra? tions of at least about 1gram per liter and pai ticle sizie less:

than about 5 microns.

'14. A bath in accordancewith claim 9 wheri i fsaiti bath-insolubleparticles are sil icon carbide particles concentrations of at leastabout :1 gram/liter a'ridfpafticle size less than about 7 microns; j

1s. A bath in accordance with 'claim 9,' wherein. sa'i i' bath-insolubleparticles are aluminum oxide particles, in. concentrations of at leastabout 1 gram/literand particle.

size less than about 5 microns.

16.. A bath in accordance withjclaim 9 iwhereinlsaidl bath-insolubleparticles are polyvinylchloride {Pl/C particles in concentrations of atleast about 1 ;gram/liter.

and particle size less than about 50 microns.

References Cited 3 TE ATENT? (Other references on followiiig pagej 1wherein said bath-insoluble particles are boron particles in concentra-5 UNITED STATES PATENTS 6 Glutamic Acid as an Addition Agent, by Adameket aL,

p. 931, The Canadian J. Chem. 32,931, 1954. 11/1950 y n OrganicChemistry by Brewster, 1961, pp. 424-425. (U62 Gllchnst O I Trans.Electrochem. Soc., vol. 54, 1928 by Pink et aL, 1,7M,927 2/ 1929Bezzenberger 204181 5 315 316 2,858,256 10/1958 Fahnoe t 1, 204 -181IKiPk-Othmer Encyclopedia of Chemical Technology,

0 2 1 a 1 1 V01. 8, 1965 pp. 30 -32. 1 970 Welgel 204 Transactions ofthe Electrochem. Society Fink et a1.

FOREIGN PATENTS 54, 1928, pp. 315320.

580,302 7/1959 Canada 20452 R 10 589,647 12/1959 Canada 204-52 R JOHNMACK Pnmary Exammer OTHER REFERENCES Modern Electroplating byLowenheirn, 2nd ed., 1918, pp. 178-479.

R. L. ANDREWS, Assistant Examiner US. Cl. X.R. 15 204-52 R, 181

